Reliquary. A space inside or behind an altar, where relics were kept. Relics were one of the main targets of the Reformation, and were destroyed with enthusiasm. However, perhaps it is surprising that so few have survived, since we may presume that a recess of this kind might have had other practical uses.
Reliquaries still exist in many Catholic churches, although they are no longer required for the consecration of an altar. Mobile reliquaries enabled the relic to be carried in procession, and some gorgeous ones can be seen in the Victoria and Albert Museum, a favourite haunt of this site. But no medieval examples survive in Norfolk parish churches.